1. Field of the Invention
The invention relates to a method of power control, to a radio terminal equipment arrangement, to radio terminal equipment and to a secondary terminal unit.
2. Description of the Related Art
Mobile devices divided into several parts that are used in various combinations are being developed. Multipart radio terminals, for example, may include a cellular core unit and a number of optimized peripheral units. The peripheral units of the multipart radio terminals are optimized for specific tasks and all the peripheral units are connected to a core unit by low-power radio frequency (LPRF) connections, such as Bluetooth connections. One of the peripheral units may be optimized for making basic phone calls and another peripheral unit may be optimized for messaging and browsing or for imaging and music, for example. Typical mobile phones may also comprise several enhancement devices, such as headsets, pens, and web pads that communicate with the mobile phone over wireless connections.
The core unit and the peripheral units of the multipart radio terminals use predetermined transmit power classes. The Bluetooth power classes are described in the Third Generation Partnership Project; Bluetooth Specification, Version 1.1, 22 Feb. 2001, p. 21 of 1084. Typically, in a mobile environment, the core unit and the peripheral units are short range LPRF equipment. Bluetooth power class 2 is meant to be used in close-range areas, where the distance between the core unit and the peripheral units is between 0 to 10 meters. Bluetooth power class 1 is meant to be used in long-range areas, where the distance between the core unit and the peripheral units is between 10 to 100 meters. Usually, however, the range between the core unit and the peripheral units is about one meter. It would thus be a waste of power to have power class 1 equipment in multipart terminals at all times. Further, more restrictions for using power class 1 are met in form of regulatory requirements due to radiation towards the human body, for example. However, in home environments, for example, the core unit may be very far away from the peripheral units, and more output power would be required to maintain a good link quality between the devices. A user of the multipart device may not wish to carry the core unit along all the time but still carries the peripheral unit(s) with him/her. This increases Bluetooth link distances and causes connection and data transfer problems with power class 2.